Obesity and its related disorders, including type 2 diabetes mellitus, metabolic syndrome, and cardiovascular disease, have reached epidemic levels in the United States. While genetic predisposition provides a background for the expression of acquired metabolic defects in obesity and type 2 diabetes, the majority of these metabolic defects become apparent only through energy imbalance, that is, energy oversupply and/or decreased energy expenditure. Therefore, gene- environment interactions are significant in the development of these diseases and there is increasing evidence that these effects are mediated biologically at the level of epigenetics, a spectrum of largely sequence-independent regulatory influences on gene expression including DNA methylation. Epigenetic influences on phenotype are perhaps best exemplified by recent studies demonstrating that the intrauterine environment, either malnutrition or overnutrition, influences gene expression through differential methylation of genes that lead to an altered metabolic phenotype that increases the risk for obesity and obesity-related disorders in the offspring. However, very little is known about the potential for epigenetic regulation of energy metabolism and obesity in adult life. An intriguing possibility is that chronic exposure to an environment that predisposes people to obesity and diabetes, such as a high fat Western diet and sedentary lifestyle, leads to altered DNA methylation and altered phenotype of metabolically active tissues. The liver is central to metabolic regulation and, as the key distributor of most ingested nutrients due to its anatomical proximity to the gut, is an ideal candidate for testing epigenetic changes from overnutrition. We propose to test the hypothesis that the development of obesity in adulthood alters gene expression and energy metabolism in the liver at least partially through changes in DNA methylation. Aim 1 is perform a quantitative genome-wide analysis of the hepatic DNA methylome following exposure to a high fat diet, which will be accomplished using Methyl-Sensitive Cut Counting (MSCC). Aim 2 is to perform a quantitative genome-wide analysis of the hepatic transcriptome following exposure to a high-fat diet, which will be accomplished using genome-wide 5'SOLID-SAGE. Aim 3 is to determine mechanistic relationships between DNA methylation and gene expression, which will be accomplished using state of the art computational approaches to identify genes that are both differentially methylated and expressed, and then selected genes will be validated with qRT-PCR and single gene methylation analysis. Finally mechanistic relationships between transcription factor recruitment and transcriptional rate will be determined by chromatin immunoprecipitation and nuclear run-on. This project has the potential to provide groundbreaking information concerning the epigenetics of obesity.

Public Health Relevance

Obesity and its related disorders, metabolic syndrome and cardiovascular disease, often have an underlying genetic component that only becomes apparent after exposure to overnutrition and/or sedentary lifestyle. This suggests that the environment plays an important role in the development of obesity, and biologically this may manifest as an epigenetic phenomenon;i.e., genetics affected at a level other than the sequence of the DNA. We propose to test the hypothesis that the development of obesity in adulthood alters gene expression and energy metabolism in the liver at least partially through changes in DNA methylation. Both DNA methylation and gene expression will be measured after a high fat diet at the level of the entire genome and at high resolution. Using state-of the art bioinformatic approaches and sophisticated molecular assays, we will then identify and validate individual genes that have changes in both methylation and expression after a high fat diet, and will determine how DNA methylation alters the recruitment of transcription factors and the rate of transcription. This project has the potential to provide groundbreaking information concerning how the environment (in this case a high fat diet) affects the genetics of obesity.